1. Field of the Invention
The present invention relates to a rolling bearing, and more particularly, it relates to a large-sized rolling bearing such as a bearing, which an average diameter of a rolling element is at least 20 mm, for a rolling mill in the steel industry.
2. Description of the Prior Art
In general, the material for a large-sized thick bearing employed in the steel industry or the like is prepared by carburized material such as SNCM815 having a large content of alloying element, in order to ensure required case depth and toughness. With SNCM 815 having a large content of Ni and requiring a high material cost, however, surface hardness is hard to attain in carburizing and a long time is required for carburizing, to disadvantageously result in a high cost for the rolling bearing and dispersion of the rolling contact fatigue life.
If the content of the alloying element is small, on the other hand, hardenability is so lowered that required hardness distribution (case depth) or core hardness cannot be obtained although the material cost is reduced.